A. Field of the Invention
A new detection principle that can image surface impedance and determine the mass to charge ratio of molecules in liquid phase and in microfluidic/nanofluidic devices.
B. Description of Related Art
Interfacial impedance spectroscopy has been widely used as a powerful technique to study various surface and electrochemical processes including electrode corrosions, electroplating and molecular adsorption and reactions. It has also been applied to chemical sensors, DNA chips, biosensors and study of cells (Katz & Willner, 2003). To date, interfacial impedance spectroscopy has been performed on a single electrode or an array of electrodes in which each electrode is individually connected to a measurement circuit. For many applications, it is highly desired to image or map the local impedance of the entire surface of an electrode, which so far has not been demonstrated. Atomic force microscopy has been used to probe local capacitance, but it rarely used for practical and routine analysis because it is slow and complicated.
To use molecular recognition for sensor applications, one has to be able to convert a molecular binding event into a signal. Based on the signal transduction mechanisms, sensors have been divided into electrical, electrochemical, optical and mechanical sensors. A good signal transduction method must be fast and sensitive, but it also highly desired to provide specific signature of the target molecules. To date, most detection principles detect a change in e.g., mass or current, associated with a molecular binding event but not capable to provide the signature or identity of the target molecule. One exception is mass spectroscopy (MS) which detects the mass to charge ratios of analytes. Since the ratio is rather unique for a molecule or fragment of molecules, MS has become a powerful method for detecting and identifying chemical species. However, MS does not work in solution phase, and miniaturization of MS for gas phase analysis faces many challenges.